Gas-filled incandescent electric lamp



Oct. 15, 1940. v SPAETH v 2,218,346

GAS-FILLED INCANDESCENT ELECTRIC LAMP Filed July 8, 1938 Patented Oct.15, 1940 UNITED STATES PATENT OFFICE 2,218,346 GAS-FILLED INCANDESCENTELECTRIC LAMP This invention'relates to incandescent electric lamps ofthe gas filled type. Its general object is to provide gas filled lampswhich shall be free from the danger of arcing between points of highpotential difference in the filament or in the light source systemwhatever it may be.

In gas filled lamps as heretofore constructed the shape and manner ofmounting the filament has been controlled to a large extent by thetendency to are which is brought about by the incidental flow ofelectrons and ions between heated portions of the filament as to whichexists a substantial potential difference whenthe lamp is energized. Forexample, it has always been necessary to support the ends of a filamentat their point of connection with the lead wires by a distancesufiicient to prevent an are striking across it, even at the expense ofwaste space in the lamp and undesirable enlargement of the filamentpattern. Similarly it has been necessary to spread or space intermediateportions of the filament and thus sacrifice an otherwise desirableconcentration of the light source.

' The tendency to archas also had the effect of restrictinglampmanufacturers to the use of a gaseous filling containing a substantialproportion of nitrogen, whereas pure argon, krypton, xenon or otherinert gases of low heat conductivity might oherwise be used to producelamps of greater luminous efficiency. Since'in a gas filled lamp pureargon aggravates or facilitates arcing it is generally restricted to notmore than 84% to 86% of the gas mixture.

The tendency to arc is especially aggravated in lamps having reflectingsurfaces therein since the electrons and ions are likely to be reflectedinto the critical spaces between points of high potential difference inthe filament and s6 assist in the formation of an are.

m The present invention rests upon my discovery that arcing may beprevented in a gas filled electric lamp by interposing a baiiie orobstacle in the path of electron flow between points of high potentialdifference in the light source system. For

5 example, I have discovered that by,interposing a plate in the spacebetween the branches of a looped filament arcing is effectivelyprevented even through the branches may be located much closer togetherthan has heretofore been regarded 50 as practicable in the manufactureof lamps. The precise character of the baffle member is of secondaryimportance so long as it is effective to interrupt the electron flowwhich would otherwise take place. It may comprise a thin metal 86 plateor a plate or block of mica, porcelain or alundum or other refractorymaterial. Preferably .it will present light reflecting surfaces in orderthat the output of the lamp may not be reduced. It may be electricallyneutral in the system or it may be connected to one side of the circuitso 5 that it will be charged and act to deflect the electrons as well asto obstruct their flow. I may employ a single baflle or a plurality ofbaffles depending upon the pattern of the light source sys-, tern. l0

Lamps employing features of the present invention present many importantand valuable advantages. In the first place, all danger of destructionof the lamp by arcing is eliminated. In the second place, the filamentor light source may 15 be concentrated and thus brought more accuratelyinto optical focus. In the third place, my invention permits the use ofpure ,or substantially pure argon, or krypton or xenon in the gaseousfilling of the lamp with an attendant increase of 20' 4% to 15% in theluminous efficiency of the lamp. All of these advantages are emphasizedin lamps of thereflector type, particularly those having an insidecoating of metallic silver or aluminum or other reflecting material inwhich, as already 25 noted, the tendency to are has always beenparticularly troublesome.

These and other features of the invention will be bestunderstood andappreciated from the following description of certain preferred embod-30 iments thereof selected for purposes of illustration and shown in theaccompanying drawing in which:

Fig. 1 is a composite view in elevation, one half v showing my inventionas embodied in a lamp hav- 35 ing a clear bulb of one size and the otherhalf showing a lamp having a silver coated bulb of a larger size. I

Figs. 2, 3, 4, and 5 are diagrammatic views showing differentarrangements of filaments equipped with electronic baflles, and

Fig. 6 is a plan view on an enlarged scale of the filament shown in Fig.1.

The right hand side of Fig. 1 shows one half of an electric lamp havinga clear glass bulb I0 .equipped with the usual metallic base I l andhollow mount l2 terminating in a solid press l3 from which projects aglass arbor M terminating in an enlarged head.- Metallic supportingwires l5 are K embedded in the head of thearbor and extend plicationSer. No. 15,605, although the material and shape of the filament are notcritical features of the present invention. The ends of the filament l6are brought close together and connected to lead-wires l1 which aresealed into the press of the mount in the usual manner.

The drawing together of the ends of the fila- 'ment i8 is permitted onlyby the employment of a baflle member between them in accordance with thepresent invention. As herein shown this baille may comprise a thin plateI8 of molybdenum, nickel or the like arranged vertically in edgewiseposition and extending substantially equal distances above and below theplane of the filament l6. As herein shown the baflle plate I! issupported by a pair of wires l9 embedded in the head of the arbor I4 andby a single forwardly inclined supporting wire 20 similarly embedded inthe head of the arbor and connected to the forward portion of the baffleplate i8. The wires 19 and 20 give the baflle plate a threepointsupport, holding it securely against vibration which might otherwisetend to break the points of connection. As already explained thefunction of the baille plate I8 is to interrupt the fiow of electronswhich would otherwise take place between the heated ends of the filamentwhen subjected to appreciable difference of potential. The effect of thebaffle I8 is to eliminate or largely reduce the flow of electronsbetween these points of the filament to such an extent that the dangerof arcing is practically obviated between the ends of the filament andbetween adjacent intermediate portions thereof.

The left side of Fig. 1 discloses one half of an electric lamp having abulb 30 provided upon one surface with a metallic reflecting coating SIof silver, aluminum or the like. The coating extends from the neck ofthe bulb to its line of maximum diameter and has the effect ofconcentrating the light of the lamp and directing it outwardly in asingle well-defined beam. In a reflecting lamp of this kind the filamentis preferably located wholly within the silvered area of the bulb asindicated in the left hand portion of Fig. 1 where the filament is shownas located entirely below the upper boundary of the metallic coating.When so located in a reflecting lamp it is good practice to dispensewith the glass arbor l4 and to support the filament upon the ends ofsupporting wires of refractory metal sealed into the press of the mount.As already explained the present invention has a particularly usefulapplication in reflecting lamps since these are more likely to arc onaccount of electrons being reflected into the critical space betweenportions of the filament between which there exists ahigh potentialdifference when the lamp is energized. A gas-filled lamp of therefleeting type equipped with a battle between a'd-.

jacent portions of the filament, as suggested in Fig. 1, thereforeconstitutes a particularly desirable and useful embodiment of thepresent invention. In Figs. 1 and 6 the filament is shown as arranged inthe form of an open loop with its ends brought relatively close togetherand separated by the baille 18. There are however many otherarrangements of filament in which the baflle of my invention may beadvantageously employed.

Some of these arrangements are illustrated in Figs. 2-5 in a somewhatdiagrammatic form. For example in Fig. 2 the filament 40 is disposedsubstantially in the shape of a V having its forward ends connected tolead wires 4| and its vertex supported by a neutral wire 42. In thisinstance the maximum drop in potential occurs between the ends of thefilament where they are connected to the lead wires M. In accordancewith the present invention an electron baffle plate 43 of suitablerefractory material is disposed edgewise between the ends of thefilament and substantially symmetrically in respect to a line betweenthem. Electron fiow between the two ends of the filament is thusinterrupted and danger of arcing eliminated. It will be apparentv thatbetween the intermediate portions of the filament located to the rear ofthe baffle plate 43 the potential danger in the circuit is reduced belowthe danger point.

In Fig. 3 the filament 50 is shown as disposed substantially in theshape of an N and connected at its ends to lead wires 5|. Theintermediate vertices of the filament may be supported in any desiredmanner. In this instance two baflle plates 52 may be provided, onelocated adjacent to each lead wire 5| and supported thereby. The baffleplates 52 as above are arranged symmetrically in respect to the plane ofthe filament 50 and project at their inner ends into the line joiningthe ends of the filamentthus effectively interrupting electron flow inthis path. It will be noted that the baflle plates 52 are notelectrically neutral when mounted upon the lead wires but are chargedwhen the lamp is energized and consequently act not only to interruptthe electron flow in a mechanical sense but alsoto repel the electronsin an electro-magnetic sense. This is because the direction of currentin the two outside branches of the filament is also in the samedirection, that is, when the current is flowin upwardly in the left handbranch as shown in Fig. 3 it is also flowing upwardly in the right handbranch. The points of maximum potential diflerence are thus separated bythe maximum dimension of the filament pattern and safeguarded by thebaffle plates as already explained, The plates 52 are however, notdirectly heated by the passage of electric current and so do notthemselves emit electrons in substantial amount, that is to say, in anamount that would induce arcing. The N shaped arrangement of filamentconstitutes a feature of the present invention whether it is employedwith a bafile plate or without one. Further, the-bafile plates, whenused, may be connected to the lead wires as shown in Fig. 3, or they mayhave insulated supports or be of non-conductive material so that theyare neutral in the system.

In Fig. 4 the filament 60 is shown as arranged in the shape of an M thetwo ends of the filament being connected to lead wires 6! and theintermediate vertices supported in any desirable manner. A baffle plate62 is disposed between the forward ends of the filament and across theline connecting the points of maximum potential difference and thesepoints thus safe-guarded against arcing. As already explained, theemployment of the bailie 62 permits arranging the filament in compactdesign and drawing together its ends close together although the maximumdrop in potential occurs between them.

In Fig. 5 the filament 10 is shown as arranged in triangular form withits ends brought inwardly toward each other and connected to lead amasaawires ii. The intermediate vertices of the filament may be supported inany desirable manner and an electron baliie plate 12 is disposed betweenthe ends of the filament and symmetrically in respect to a line joiningthem. In this instance the transverse branches of the filament may bedeflected if desired and disposed obliquely with respect to a transverseplane passing through its points of connection with the lead wires. Forexample, one of the end sections of the filament may be inclinedupwardly from its point of connection with one lead wire and the otherend section may be inclined downwardly from its respective point ofconnection, instead of being disposed in alignment with the otherfilament section.

In certain types of lamps the filament may be U-shaped and located withits axis coinciding with the major axis of the lamp. In such a lamp theelectronic baiile will be located in the bight or loop of the filamentand between its ends. Similarly, the intermediate section of an N-shaped filament may be deflected in a curve out of the plane of the endsections thus afl'ording space in its bight for a battle located betweenthe points of connection with the lead wires.

While it is of course well recognized that there can be no arcing in aperfect vacuum, nevertheless even in a so-called vacuum lamp there maybe gases present in small quantities, these gases originating from thewater vapor or from some other source and being sufilcient under certaincircumstances to cause an arc. It must therefore be understood that myinvention contemplates the use of a battle in any lamp which has even avery insignificant quantity of gas present but in which arcing mightconceivably take place if my bafiie were not used in connection with thewires secured to the ends of the filament, and an electron baiiiedisposed between the ends of the filament and having reflecting surfacesfor di recting rays from the filament outwardly in the bulb and fordirecting electrons coming from the reflecting coating away from thespace between the ends of the filament.

2. An electric lamp comprising a gas-filled bulb provided with an innersilver reflecting coating, a filament therein, and an electron bafiie inline with points of high potential difference in the filament and havinga reflecting surface for directing electrons coming from the reflectingcoating away from the space between said points of high potentialdifference in the filament.

4. A reflecting electric lamp comprising a bulb having a partialinternal reflecting surface, a filament having branches extending intoproximity to each other, lead wires connected to the ends of thefilament and a single intermediate baffle plate located substantiallymidway between the ends of the filament and having reflecting surfacesfor directing rays from the filament outwardly in the field of the lampand for directing electrons coming from the reflecting coating away fromthe space between the ends of the filament.

, 5. An electric lamp having a gas filled bulb provided with a partialmetallic reflecting coat-

